A Sm-Co based magnet is known as a rare-earth magnet having improved heat resistance, but is expensive. The term "heat resistance" as referred herein particularly signifies that the magnetic force of the magnet does not degrade by heat. As disclosed in Japanese Patent Public Disclosure No. 4-116144 (Patent No. 2740981), one of inventors of the present invention and others have proposed a R--B--C--Co--Fe based permanent magnet alloy as a rare-earth magnet reduced in cost and yet improved in heat resistance. This magnet alloy contains carbon (C) as an essential alloy element, and utilizes a combination of a light rare-earth element and a heavy rare-earth element for the rare-earth element (R). The disclosure teaches that the irreversible demagnetization of the magnet alloy is improved remarkably (i.e., the negative irreverible demagnetization values approach 0%) by the incorporation of C, and that the irreversible demagnetization is further improved by partly incorporating a heavy rare-earth element for R.